The present invention relates to eyewear, and more particularly relates to retaining a lens in an eyewear frame.
Eyewear frames have traditionally been formed from either a shaped metal wire or a molded polymer, with either a glass or polymeric lens (unitary or dual) being fitted to the frame. Retaining a lens in the frame requires that the lens fit the frame with as close a tolerance as possible so that the lens does not unintentionally release from the frame. While a close tolerance is desired, it is also important that no damaging or distorting stresses be placed on the lens, whether it be a corrective (Rx) or non-corrective lens. It is furthermore many times desired that the lens be replaceable upon the frame to permit replacement of a damaged lens, or switching by the consumer between different types of lenses (e.g., lenses having different coatings) on the same frame.
It will be appreciated that these criteria are competing in the respect that optimizing one of the criteria tends to de-optimize one or both of the other criteria. This is especially evident when one considers the plethora of alternate lens-retention techniques disclosed in the prior art which strive to optimize all three of these criteria in one design. Some known lens-retention techniques used with traditional frame constructions, including those of the split-frame, continuous rim, semi-rimless, and rimless type, are as follows.
In metal wire frames, a split-frame configuration is common. In this construction, a metal eyewire is formed by passing a wire feedstock through appropriate dies which form the wire into the desired cross-section. At this time, an eyewire groove, usually V-shaped in section, is formed wherein the bevel of the lens edge is fit. The eyewire is then passed through a bending station wherein it is bent into the desired outline and is then cut, thereby leaving two free ends to which are brazed or soldered endpieces or "rim locks" as they are termed in the art. The eyewire is separable at the free ends thereof to permit opening of the eyewire a distance sufficient to permit insertion of the lens, with the eyewire then closed about the lens and the free ends thereof secured together with a screw which extends through the endpieces on the eyewire. A protective gasket or adhesive is sometimes applied between the groove and lens edge. See, e.g., U.S. Pat. Nos. 3,824,006 to Voit; 4,340,282 to Murakami; and 4,427,271 to Bausch & Lomb Incorporated (applicant herein).
In semi-rimless frame constructions, one commonly used method of retaining the lens in the frame uses a strong, thin cord which is fixed at one end of the frame, wraps under the bottom edge of the lens while engaging a groove formed in the bottom lens edge. The other end of the cord is then releasably fixed to the other side of the frame, thereby securing the lens to the frame. See, for example, U.S. Pat. No. 4,842,399.
In rimless eyewear constructions, a front frame is absent, and the lenses are directly attached to the temple and bridge components of the eyewear. In this type of construction, holes or other openings are usually formed in the lens wherethrough fastening devices are passed to secure the components together. See, for example, U.S. Pat. Nos 2,208,103, 2,588,505 and 2,668,291.
Still other lens-retaining methods feature either a recessed portion or a projection formed on the edge of the lens which mates with a complementary feature on the frame. See, e.g., U.S. Pat. Nos. 4,834,523 to Porsche; 5,523,804 to ;5,387,949 to Oakley, Inc.; and 5,400,089 to Essilor. While mechanically strong, this type of lens securement requires machining or molding complex features on the lens and frame which are expensive to manufacture.
In plastic frame eyewear, a continuous rim frame construction is common. In this type of frame, the lens is snapped into the respective eye opening of the plastic frame, usually with the use of heat to temporarily expand the plastic frame. This is known in the art as tension mounting, which is usually not possible with non-yielding metal frames. As with metal eyewire frames, however, the beveled edge of the lens fits within a groove formed in the perimeter of the eye opening. See, for example, U.S. Pat. Nos. 3,884,561 and 4,196,982.
Another lens-retention method used in continuous rim type frames (of both plastic and metal construction) uses either a rigid or flexible retaining ring which follows the contour of the lens opening in the frame, and is fit against the lens in the frame, sandwiching the lens edge between the frame and retaining ring. The retaining ring itself is secured to the frame by either a press-fit or with an adhesive, for example. See, e.g., U.S. Pat. Nos. 3,552,840 to Braget; 3,958,867 to Morgan; 5,541,674 to Oakley, Inc.; and French Pat. No. 1,126,329. The problem remains, however, that the retaining ring would be an added expense to the manufacturing process, especially since it must be very closely matched to the contour of the eye opening to provide a secure fit. The retaining ring itself could also unintentionally release from the frame, thereby allowing the lens to fall from the frame.
Yet another example of lens retention in a continuous plastic frame is seen in U.S. Pat. No. 4,135,792 issued to American Optical Corporation on Jan. 23, 1979. The passage found therein beginning at Col. 2, In. 59 and ending at Col. 3, In. 8 describes a lens retaining method wherein the eye openings of the frame are provided with an "L" shape cross-section providing a flat lens-receiving seat 24. Lens 16 is provided with a matching flat edge about the full periphery thereof and cemented in place with an epoxy or other plastic cement. Since the invention of the '792 patent is directed toward a plastic frame and plastic lens each having the same or lower tensile elastic modulus, the specification further states: "Problems relating to conventional differential expansion of spectacle frame fronts and lenses having been obviated, a secure and permanent connection between lens and frame can thus be accomplished." The lens retention method of the '792 patent is therefore limited to plastic: frames and plastic lenses of the type disclosed therein since the matching flat edges of the lens and lens-receiving seat of the frame cannot accommodate differential expansions and contractions of the frame with respect to the lens. It is furthermore evident that the matching flat edges of the lens edge and frame would complicate even curing of the epoxy, especially if the material is of the UV-curable type since UV light would not be able to penetrate the lens and frame uniformly, if at all, to reach the epoxy layered between the flat lens edge and frame. Still another potential problem is the inability to control the thickness of the epoxy layer, which in this instance is dictated by the difference between the diameter of the lens and that of the frame opening.